Abstract

As part of a continental-scale series
of drought reconstructions, Cook et al (1999) conducted dendroclimatological
research that included the development of a ring-width oak chronology
in northeastern Ohio extending from the seventeenth century to
1985. The information contributed to the development of tree ring
PDSI reconstructions that are used for interpretation of past
climate variation, particularly drought. The purpose of the present
study is to extend the chronology further back into time and also
update it for the last fifteen years. Using Cook et al's (1999)
Johnson Woods data for comparison, a separate, independent pool
of data was collected. Three visits to Johnson Woods were used
for coring fallen logs and for collection of several sections
of trees cut previously by a chainsaw. These samples not only
bolstered the data from Cook et al (1999) study by adding substantial
sample size, but also effectively extended the chronology, from
1605 through 1999.

Johnson
Woods is a Ohio Department of Natural
Resources Nature Preserve. Sampling was done in cooperation with
the Ohio Department of Natural Resources Division of Natural Areas
and Preserves. The tree cores and sections from this study and
the data are archived at The College of Wooster Tree Ring Lab
housed in the Department
of Geology.

Introduction

Tree rings have been very useful tools
in many places around the world for the study of landscape erosion
and for the dating of structures and other items that contain
wood. Tree rings are also used extensively as indicators of past
climate. The field of tree ring study that deals with climate
is called dendroclimatology. First developed A.E. Douglass, Waldo
S. Glock, and Edmund Schulman, the field uses variations in annual
growth rings in trees in order to draw conclusions about climatic
variation within a geographic area. In many areas around the United
States, and indeed around the world, there exists modern meteorological
observational records for at most, the last 100 years, that are
used by dendroclimatologists in correlation to tree ring data.
These two pieces of data, tree ring and meterological records,
can be used together in order to make reconstructions of past
climate that will show variations in temperature or moisture.
This information is valuable not only for development of paleoclimatic
models, but also for agricultural contingency planning (Cleaveland
et al 1992).

Tree Growth and Ring Formation

In woody plants such as trees, there
is a process of development that must occur in order for the undefined
cambium to differentiate into new and deceased wood cells. The
method by which this occurs is cell division. A plant cell is
distinct from animal cells mainly bcause of the presence of a
cell wall. Inside this wall, exists the protoplast, various organs
such as golgi-vesicles, dityosomes, mitochondrion, an endoplasmic
reticulum, and ribosomes. Dictyosomes are very helpful in the
formation of a cell wall during cell division. During this process
of cell wall formation, three fibrous layers are created to make
up this final wall. Before the walls thicken fully, the cell expands
so that the fibers become intertwined. The structure of the cell
wall depends entirely on the function the cell performs for the
plant.

From this single plant cell, differentiation
occrs. At this point, the apical meristem develops a plant body
whose cells on the tips of its roots and sprouts are the first
to divide. Layers of cells eventually develop, and from these
layers, the entire woody plant surrounding the stem begins to
protect it like a coat. This new structure is called the cambium.
Through continued development, xylem begins to form on the inside
of this cambium, and phloem grows around the outside of it (Figure
1). The stem of the plant now begins to grow in two directions,
anticlinal growth occurs to increase the size of the plant vertically,
and periclinal growth occurs to increase the radius horizontally
(Schweingruber 1996). In the xylem, two functions are performed,
providing support for the tree, and conducting water through the
plant.

Figure 1: Three dimensional
arrangement of cell elements in the xylem and phloem of dicotylodenous
(deciduous) wood. From Schweingruber (1996).

Principles of Dendrochronology

There are nine basic principles that
are accepted as being imperative to the proper study of tree rings.
These principles have been formulated through repeated observations
and experience in studies from around the world.

For a complete discussion of these principles,
click on the log below!

Oak Rings and Structure

During a year in a tree's growth a single
ring is produced. This ring contains two major divisions, referred
to as early wood and late wood. Early wood is the first growth
which a tree puts on during its growing season. In northeastern
Ohio oaks, this begins in early spring, usually early April. This
growth continues and advances into the late wood growth during
the summer. In many trees, the difference between these two parts
of a ring can be as subtle as a slight change in color. However,
in hardwoods such as oak or elm, these two parts are quite distinct.
The early wood in these trees contains very large vesicles, whereas
the late wood does not (Figure 2).

Figure 2: A cube of wood from
oak or elm.

Method

Oak trees in northeastern Ohio are quite
common, but old growth oak trees are very uncommon. These old
growth oaks can live to be up to 400 years old. These are dying
out however, and are being replaced by beach-maple forests in
most of the region. One of these last remaining stands of old
growth oak forest in northeastern Ohio is Johnson Woods, a 200
acre piece of land that lies just a few miles north of the city
of Orrville, Ohio, Wayne County. One previous study in this wood
was conducted by Cook
et al (1999).

The purpose of the present study was
to extend Cook et al's (1999) data back into time, and to update
it for the last fifteen years. To do this, thirty-one trees were
sampled, producing forty-five usable ring width series. Some trees
were sampled more than once in order to minimize variations in
ring widths around the circumference. Samples were taken from
trees that were mainly lying dead on the forest floor. Some of
these were found to have been dead for up to sixty years. One
sample, JW0100, was a section cut by a chainsaw recently that
was found on the forest floor.

These samples were taken back to the
tree ring laboratory at the College of Wooster, Ohio, for preparation
and analysis. Cores were taken out of the straws, and mounted
into poplar grooved mounting sticks with wood glue. These were
then left to dry overnight. Sanding occurred next, and was begun
with 50 grit paper, progressively sanding to a grit of 600, leaving
a highly clear surface. Next, rings were counted under a dissecting
microscope, and marked in the standard way with one pencil dot
per decade, two per half-century, and three per century. Ring
widths were measured using a digital devise with a precision of
0.001mm, and recorded as Edit II files. Crossdating was performed
with the aid of COFECHA (Holmes, 1983) and raw data was processed
into ring-width chronologies using the ARSTAN method (Cook, 1985).

Discussion

Figure 3: The standard
ring width data from Johnson Woods, OH. Sample size is depicted
at the bottom of the graph

(graph by R. Kohrs).

Figures 4-6: These are linked
to the larger versions of the raw, arstan, and residual data from
Johnson Woods, OH

(graphs by R. Kohrs)

The data that was analyzed for this study
correlated well with the data collected for the previous study
conducted by Cook et al (1999). Figure 3 presents the most interesting
information. This graph depicts sample size in conjunction with
the normalized ring width data and a weighted mean curve. This
type of graph is very useful for viewing the entire picture of
the northeastern Ohio climate over the last 400 years, and also
provides insight into the quantity of data that was available
for the following conclusions to be drawn. From AD 1700 on, a
strong sample size exists, and thus the record is considered reliable.
A weighted mean curve was added to the graph so that the oscillations
in record can be better observed.

This variations in this graph (Figure
3) are primarily a record of growing season moisture based on
previous studies. The period of 1850-1899 was a time of apparently
high moisture. The twentieth century does not appear to have been
the driest period of time for the area. The early nineteenth century
appears to be the driest interval of the entire record. There
appear to be no obvious patterns in this drought record over the
last 300 years.

Graphs 4-6 show various different depictions
of the same tree ring data, in order to isolate different attributes
of growth over the last 400 years.

Future Work

There is more that can be done with Johnson
Woods. It would be very useful to attempt to increase the sample
volume for the period of 1600-1700. A period of 400 years would
allow patterns in the data, if they exist, to possibly come to
light. This study of Johnson Woods could also lead to fruitful
studies of some of the other remaining old growth forests in Ohio
such as Hueston Woods near Cincinnati. Eventually, a useful drought
record for the state of Ohio and nearby regions may be created.

Check out some of these pics
of Dr.
Greg Wiles (the guy I worked for) and
I doing some serious climate research!

Here's Greg coring a dead log.
Tired yet? What's that? Did you say that the borer was stuck?!